The benzotriazoles have long been an important class of UV absorbers and have gained wide commercial importance and acceptance for many industrial applications. The prior art is replete with references to their manufacture and utility. However, as requirements become ever more stringent and demanding, the search for still more stable and durable benzotriazoles continues. The gradual phase out of HAPS solvents, such as xylene, because of environmental concerns and their replacement with non-HAPS solvents, such as esters, ethers or ketones, and increased durability requirements for automotive coatings make this search more urgent. Indeed, the automotive industry is most concerned about UVA losses from automotive paints and coatings as seen in the publication by J. L. Gerlock et al., Proc. 36th Annual Tech. Sym. (Cleveland Coating Society), May 18, 1993.
Vysokomol Soedin, Ser. A, 18(3), 553 (1976) describes the linear dependence of hydrogen bond strength and photostability in benzotriazoles.
J. E. Pickett et al., Angew. Makromol. Chem. 232, 229 (1995) describe the photodegradation of benzotriazole UV absorbers in poly(methyl methacrylate) films. Structural variation generally caused only small differences in the rates of degradation unless the substitution disrupted the intramolecular hydrogen bonds which are critical for stability. Pickett et al. did not test any benzotriazoles containing both electron withdrawing and electron donating groups as in the instant invention.
The prior art leads one to the conclusion that strengthening the hydrogen bond leads to a more stable benzotriazole, but does not teach how this can be accomplished. The instant invention discloses benzotriazoles which exhibit enhanced durability, but surprisingly this enhanced durability is not always related to greater hydrogen bond strength. Indeed, compounds with enhanced durability often have weaker, not stronger hydrogen bonds
U.S. Pat. Nos. 4,226,763; 4,278,589; 4,315,848; 4,275,004; 4,347,180; 5,554,760; 5,563,242; 5,574,166 and 5,607,987 describe selected benzotriazoles, substituted in the 3-position of the hydroxyphenyl ring by an .alpha.-cumyl group, which show very. good durability in automotive coatings. These benzotriazoles represent the present state of the art. The instant invention is directed at preparing benzotriazoles which exhibit still better durability and low loss rates from the prior art benzotriazoles.
U.S. Pat. Nos. 5,278,314; 5,280,124; 5,436,349 and 5,516,914 describe red-shifted benzotriazoles. These benzotriazoles are substituted in the 5-position of the benzo ring by thio ethers, alkylsulfonyl or phenylsulfonyl moieties. Red-shifting the benzotriazoles is desirable for spectral reasons. A group at the 5-position which is also electron withdrawing provides additional benefits in low loss rates and durability as found in the instant invention.